We plan to purify and characterize the trithionate reductase system of Desulfotomaculum nigrificans. This system is composed of two protein fractions, one of which is bisulfite reductase (P582). The other fraction, tentatively designated as TR-1, is partially purified at this time. We plan to purify this protein and determine the mechanism of trithionate reduction to thiosulfate. We plan to investigate the lactic dehydrogenase (LDH) of Desulfovibrio vulgaris. By employing the methylene blue reduction assay, we hope to extensively purify this enzyme and determine several physicochemical properties. If the natural electron carrier is elucidated, we shall attempt to couple the oxidation of lactate with subsequent reduction of an electron accepting system. The systems to be tested will include adenylyl sulfate reductase as well as the enzymes participating in the dissimilatory bisulfite reduction pathway.